I think it’s possible for someone to have room for improvement without that meaning they’re crap etc.
I think O’Nien’s general positioning for the first goal was ok. He was in the right area, and reasonably close to his man.
The problem I feel was with his body shape, which I think was due to him arriving in the right position a little late. He was kind of trying to get around the back of the attacker, body at a diagonal, somewhat off balance. He’s not the biggest guy anyway, but his head was like 5 feet off the ground when the ball was headed into the net.
I think a better defender would’ve been tight with the attacker, stood tall or jumping. It still might’ve been a goal but it would’ve been more difficult for the striker.
None of this makes Luke a shit footballer or a bad person.